# unsure about using the hold on funciton

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Nevin Pang on 19 Mar 2019
Commented: Nevin Pang on 19 Mar 2019
hi, i'm still new to matlab and im unsure of how to use the hold on command.
After running the code, i'd like to produce a graph with multiple results from my code but im unsure how to use the hold on function (ie; where to put within the code)
(mulitple results as in, i'm using the limits from 0-9, 9-15 etc as listed in the above code as t and the equations x1 thru 10.
t = 0:0.1:9;
N = length(t)-1;
y = (-(1.37)*t.^2)+6000; %eqn 1
%Spline Equations
%The equations are substituted into the code.
%y1 (-(1.37)*t.^2)+6000; 0<=t<=9 0:0.1:9;
%y2 (0.943*(t-9).^2)-(24.99*t+6113.91); 9<=t<=15 9:0.1:15;
%y3 (-(0.6054)*(t-15).^2)-((13.34*t)+5975.1); 15<=t<=39 15:0.1:39;
%y4 (-(6.1557)*(t-39).^2)-((960.74*t)+7254.97); 39<=t<=49 39:0.1:49;
%y5 (5.622*(t-49).^2)-((183.8*t)+12673.95); 49<=t<=57 49:0.1:57;
%y6 (2.4008*(t-57).^2)-((93.89*t)+7903.9); 57<=t<=69 57:0.1:69;
%y7 (-(12.91)*(t-69).^2)-((36.27*t)+4273.63); 69<=t<=74 69:0.1:74;
%y8 (3.091*(t-74).^2)-((92.92*t)+8324.598); 74<=t<=81 74:0.1:81;
%y9 (0.2117*(t-81).^2)-((49.64*t)+4969.84); 81<=t<=96 81:0.1:96;
%y10 (-(5.0625)*(t-96).^2)-((43.28*t)+4407.744); 96<=t<=100 96:0.1:100
% The unknowns are 3*N with ao=0 "Linear Spline"
% Filling Matrix from point matching
V = [0;zeros(2*N,1);zeros(N-1,1)];
Z = zeros(length(V),length(V));
j=1;
f=1;
for i=2:2:2*N
Z(i,f:f+2) = [t(j)^2 t(j) 1];
V(i) = y(j);
j = j+1;
Z(i+1,f:f+2) = [t(j)^2 t(j) 1];
V(i+1) = y(j);
f = f+3;
end
% Filling Matrix from smoothing condition
j=1;
l=2;
for i=2*N+2:3*N
Z(i,j:j+1) = [2*t(l) 1];
Z(i,j+3:j+4) = [-2*t(l) -1];
j = j+3;
l = l+1;
end
% Adjusting the value of a1 to be zero "Linear Spline"
Z(1,1)=1;
% Inverting and obtaining the coeffiecients, Plotting
Coeff = Z\V;
j=1;
for i=1:N
curve=@(l) Coeff(j)*l.^2+Coeff(j+1)*l+Coeff(j+2);
ezplot(curve,[t(i),t(i+1)]);
hndl=get(gca,'Children');
set(hndl,'LineWidth',2);
j=j+3;
end
scatter(t,y,50,'r','filled')
figure (1)
xlim([min(t)-2 max(t)+2]);
ylim([min(y)-2 max(y)+2]);
xlabel('x');
ylabel('y');
grid on
grid minor
hold on
i placed a hold on at the end but i am not able to collate the results on one graph.
any help would be appreciated!
thank you!!
You should get into the habit of always using the full syntax for hold and plotting instructions, with an explicit axes handle, e.g.
figure; hAxes = gca;
plot( hAxes,... )
hold( hAxes, 'on' )
scatter( hAxes,...)

Sajeer Modavan on 19 Mar 2019
clear
clc
close all
t = 0:0.1:9;
N = length(t)-1;
y = (-(1.37)*t.^2)+6000; %eqn 1
%Spline Equations
%The equations are substituted into the code.
%y1 (-(1.37)*t.^2)+6000; 0<=t<=9 0:0.1:9;
%y2 (0.943*(t-9).^2)-(24.99*t+6113.91); 9<=t<=15 9:0.1:15;
%y3 (-(0.6054)*(t-15).^2)-((13.34*t)+5975.1); 15<=t<=39 15:0.1:39;
%y4 (-(6.1557)*(t-39).^2)-((960.74*t)+7254.97); 39<=t<=49 39:0.1:49;
%y5 (5.622*(t-49).^2)-((183.8*t)+12673.95); 49<=t<=57 49:0.1:57;
%y6 (2.4008*(t-57).^2)-((93.89*t)+7903.9); 57<=t<=69 57:0.1:69;
%y7 (-(12.91)*(t-69).^2)-((36.27*t)+4273.63); 69<=t<=74 69:0.1:74;
%y8 (3.091*(t-74).^2)-((92.92*t)+8324.598); 74<=t<=81 74:0.1:81;
%y9 (0.2117*(t-81).^2)-((49.64*t)+4969.84); 81<=t<=96 81:0.1:96;
%y10 (-(5.0625)*(t-96).^2)-((43.28*t)+4407.744); 96<=t<=100 96:0.1:100
% The unknowns are 3*N with ao=0 "Linear Spline"
% Filling Matrix from point matching
V = [0;zeros(2*N,1);zeros(N-1,1)];
Z = zeros(length(V),length(V));
j=1;
f=1;
for i=2:2:2*N
Z(i,f:f+2) = [t(j)^2 t(j) 1];
V(i) = y(j);
j = j+1;
Z(i+1,f:f+2) = [t(j)^2 t(j) 1];
V(i+1) = y(j);
f = f+3;
end
% Filling Matrix from smoothing condition
j=1;
l=2;
for i=2*N+2:3*N
Z(i,j:j+1) = [2*t(l) 1];
Z(i,j+3:j+4) = [-2*t(l) -1];
j = j+3;
l = l+1;
end
% Adjusting the value of a1 to be zero "Linear Spline"
Z(1,1)=1;
% Inverting and obtaining the coeffiecients, Plotting
Coeff = Z\V;
j=1;
fig = figure;
scatter(t,y,50,'r','filled'),hold on
for i=1:N
curve=@(l) Coeff(j)*l.^2+Coeff(j+1)*l+Coeff(j+2);
ezplot(curve,[t(i),t(i+1)]);
hndl=get(gca,'Children');
set(hndl,'LineWidth',2);
j=j+3;
end
xlim([min(t)-2 max(t)+2]);
ylim([min(y)-2 max(y)+2]);
xlabel('x');
ylabel('y');
grid on
grid minor
Please let me know if you are looking different, if you are using latest matlab you can replaceezplot with fplot and adjust color of line to single color
eg:
replace: ezplot(curve,[t(i),t(i+1)]);
fplot(curve,[t(i),t(i+1)],'color','k');
Nevin Pang on 19 Mar 2019
thank you for the help!